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User processes may require many events and when they do the cache performance of a byte index status check is less ideal than a bit index. The previous event limit per-page was 4096, the new limit is 32,768. This change adds a bitwise index to the user_reg struct. Programs check that the bit at status_bit has a bit set within the status page(s). Link: https://lkml.kernel.org/r/20220728233309.1896-6-beaub@linux.microsoft.com Link: https://lore.kernel.org/all/2059213643.196683.1648499088753.JavaMail.zimbra@efficios.com/ Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
103 lines
2.0 KiB
C
103 lines
2.0 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Copyright (c) 2021, Microsoft Corporation.
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*
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* Authors:
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* Beau Belgrave <beaub@linux.microsoft.com>
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*/
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#include <errno.h>
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#include <sys/ioctl.h>
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#include <sys/mman.h>
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#include <fcntl.h>
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#include <stdio.h>
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#include <unistd.h>
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#include <asm/bitsperlong.h>
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#include <endian.h>
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#include <linux/user_events.h>
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#if __BITS_PER_LONG == 64
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#define endian_swap(x) htole64(x)
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#else
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#define endian_swap(x) htole32(x)
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#endif
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/* Assumes debugfs is mounted */
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const char *data_file = "/sys/kernel/debug/tracing/user_events_data";
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const char *status_file = "/sys/kernel/debug/tracing/user_events_status";
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static int event_status(long **status)
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{
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int fd = open(status_file, O_RDONLY);
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*status = mmap(NULL, sysconf(_SC_PAGESIZE), PROT_READ,
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MAP_SHARED, fd, 0);
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close(fd);
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if (*status == MAP_FAILED)
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return -1;
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return 0;
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}
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static int event_reg(int fd, const char *command, long *index, long *mask,
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int *write)
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{
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struct user_reg reg = {0};
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reg.size = sizeof(reg);
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reg.name_args = (__u64)command;
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if (ioctl(fd, DIAG_IOCSREG, ®) == -1)
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return -1;
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*index = reg.status_bit / __BITS_PER_LONG;
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*mask = endian_swap(1L << (reg.status_bit % __BITS_PER_LONG));
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*write = reg.write_index;
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return 0;
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}
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int main(int argc, char **argv)
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{
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int data_fd, write;
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long index, mask;
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long *status_page;
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struct iovec io[2];
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__u32 count = 0;
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if (event_status(&status_page) == -1)
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return errno;
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data_fd = open(data_file, O_RDWR);
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if (event_reg(data_fd, "test u32 count", &index, &mask, &write) == -1)
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return errno;
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/* Setup iovec */
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io[0].iov_base = &write;
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io[0].iov_len = sizeof(write);
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io[1].iov_base = &count;
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io[1].iov_len = sizeof(count);
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ask:
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printf("Press enter to check status...\n");
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getchar();
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/* Check if anyone is listening */
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if (status_page[index] & mask) {
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/* Yep, trace out our data */
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writev(data_fd, (const struct iovec *)io, 2);
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/* Increase the count */
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count++;
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printf("Something was attached, wrote data\n");
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}
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goto ask;
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return 0;
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}
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